The present invention relates to a method and a system for controlling a work machine.
The term “work machine” comprises different types of material handling vehicles like construction machines, such as a wheel loader and a dump truck (such as an articulated hauler). A work machine is provided with a bucket, container or other type of work implement for carrying/transporting a load. Further terms frequently used for work machines are “earth-moving machinery”, “off-road work machines” and “construction equipment”.
In connection with transportation of heavy loads, e.g. in contracting work, work machines are frequently used. A work machine may be operated with large and heavy loads in areas where there are no roads, for example for transports in connection with road or tunnel building, sand pits, mines and similar environments.
A work machine is often used in a repeated work cycle. The term “work cycle” comprises a route of the work machine (ie the work cycle travel path) and a movement of a work implement, such as a bucket, (lifting/lowering operation). The work cycle is repeated in the same geographical area. During the performance of the work cycle, the work machine often encounters different gradients of the ground (uphill and downhill), and turns (cornering).
According to a first work cycle example, a wheel loader typically drives into a heap of material, lifts the bucket, reverses out of the heap, turns and is forwarded towards a dump truck where it unloads the material onto the container of the dump truck. After unloading, the wheel loader returns to the starting position.
A second work cycle example for a wheel loader is the so called “load & carry cycle” with a small ramp at the end. According to this example, material is collected in the bucket, the wheel loader is reversed, turned and forwarded a longer distance (100-400 meters) to a crusher or conveyor belt, which is located on top of the ramp, and the bucket is emptied. The wheel loader is thereafter driven back again.
According to a third work cycle example, a dump truck is loaded at a first position, driven along a varied route, unloaded at a second position and driven back along the varied route. Normally, an excavator or wheel loader loads the container of the dump truck at the first position.
The invention will be described below for a wheel loader. This should be regarded as a non-limiting example of a work machine. The wheel loader comprises a powertrain for propelling the machine via the wheels. A power source, such as an internal combustion engine, and especially a diesel engine, is adapted to provide the power for propelling the wheel loader. The wheel loader further comprises a hydraulic system for performing certain work functions, such as lifting and tilting a work implement and steering the machine. The power source is also adapted to provide the power for controlling the hydraulic work functions. More specifically, one or more hydraulic pumps are driven by the power source in order to provide hydraulic actuators (such as hydraulic cylinders) with pressurized hydraulic fluid.
The invention is particularly directed to a hybrid electric wheel loader. A hybrid electric wheel loader comprises an energy storage means, such as a battery or a capacitor (preferably a super capacitor). A problem is to control a state of charge (SOC) of the energy storage means during operation in an efficient way in order to optimize energy recovery and reduce fuel consumption.
It is desirable to optimize energy recovery and/or reduce fuel consumption of a work machine during operation.
According to an aspect of the present invention, a method is provided for controlling a work machine during operation in a repeated work cycle comprising the step of controlling transfer of power to and from an energy storage means in the work machine according to a predetermined control strategy, which is adapted for characteristics of the work cycle.
The work cycle characteristics may regard a work machine internal characteristic, such as a work machine behaviour, and/or an external characteristic, such as a work cycle travel path direction. More specifically, the characteristics may comprise a predicted and/or experienced sequence of events that takes place during performance of the work cycle and which is relevant for the control of the work machine.
Knowledge of the work cycle creates conditions for reliably predicting forthcoming events (occurrences) in the work cycle and operating the power transfer to and from the energy storage means in an efficient way. Such work cycle knowledge may be achieved either from a previously performed lap of the specific work cycle and/or from pre-available information of the work cycle, such as topographical maps.
According to a preferred embodiment, the control strategy comprises information indicative of an amount of energy required for a certain portion of the work cycle. The information may regard for example a work machine behaviour, a work cycle travel path direction and/or a work implement operation. More specifically, the information may comprise a predicted and/or experienced sequence of events that takes place during performance of the work cycle and which is relevant for the control of the work machine. Each such event represents an important change in a work machine operational parameter, and each event is preferably associated to a position along the work cycle travel path. Therefore, according to a preferred example, the energy information is based on a change in a work cycle travel path. Preferably, the energy condition is based on a change of direction of a work cycle travel path in a horizontal plane and/or on a change of ground inclination of a work cycle travel path.
According to a further preferred embodiment, the method comprises the step of controlling power transfer to and from at least one power consuming system in the work machine. The power consuming system may comprise a powertrain for propelling the work machine and/or a hydraulic system for moving a work implement of the work machine.
According to a further preferred embodiment, the method comprises the step of determining at least one condition that is indicative of an amount of energy required for a certain portion of the work cycle, and establishing the energy control strategy on the basis of said energy condition.
The energy control strategy (or energy control model) is built up on the basis of the condition variation. More specifically, the condition variation is associated to a variation in the work machine operational characteristics. In other words, the sequence of events is built up in response to the predicted and/or experienced driving pattern along the work cycle route.
According to a further development of the last-mentioned embodiment, the method comprises the step of detecting at least one operational parameter during operation of a work machine in the work cycle in question, and determining the energy condition on the basis of a magnitude of the detected operational parameter.
Preferably, the method comprises the step of repeatedly detecting said at least one operational parameter. Further, a plurality of operational parameters is preferably detected, such as an operational parameter indicative of a change of direction of the work cycle travel path. Said at least one operational parameter is preferably substantially continuously repeatedly detected.
Thus, an event may be established on the basis of the detected operational parameter in a previously performed work cycle and used for controlling a work machine by means of the control strategy in a later performed work cycle. More particularly, an individual work machine may be adapted to learn from past experiences. For example, driving patterns with regard to steering wheel deflection, gas pedal operation, brake pedal operation, work implement operation etc are recognized and stored. Further, a traveling distance for the specific work cycle is detected and the time/position when lifting force is required are recognized and stored. According to one example, the control strategy is solely determined based on driving pattern information achieved from sensors in the work machine.
According to an alternative, or complementary embodiment, the method comprises the step of predicting at least part of the energy condition on the basis of pre-available information of the work cycle in question. Such information may be formed by geographical maps of the area covering the work cycle travel path, knowledge of the specific work cycle travel path (comprising turns and slopes), the material to be transported, ground conditions, weather conditions etc. For example, a global navigation satellite system (GNSS) (such as the GPS) may be used for establishing the work cycle travel path. According to further alternatives, radio, radar, ultrasound, laser scanning, image recognition, or gyroscope-based determination systems may be used.
According to one example, the control strategy is established on the basis of both detected operational parameters while performing the work cycle and available information of the work cycle in question. Thus, the work cycle route may be indicated in a topographical map, wherein turns and slopes are defined. The control strategy is based on such a topographical map and it may be modified based on detected operational conditions.
According to a further preferred embodiment, the control strategy comprises a plurality of control steps, wherein each step is established on the basis of the condition variation. Preferably, the work cycle travel path comprises a plurality of positions, wherein each position is established on the basis of the condition variation.
Each control step indicates that the work machine should be effected for an optimum control. Such a control step may be indicated by the position of a change in altitude, or a change in direction, of the work cycle travel path.
It is also desirable to achieve a system adapted for an optimized energy recovery and/or reduced fuel consumption of a work machine during operation.
According to an aspect of the present invention, a system is provided for controlling a work machine during operation in a repeated work cycle comprising means for controlling transfer of power to and from an energy storage means in the work machine in according to a predetermined control strategy, which is adapted for the characteristics of the work cycle.
Other advantageous embodiments of the invention and its associated advantages are apparent from the following description.